DESCRIPTION ( applicant's abstract): The disruption of sleep is a widespread problem among children and is one of the most common concerns parents have about their children's behavior. Sleep problems early in life tend to persist into older ages, and sleep disorders can be severe in children with neurological or psychiatric pathologies. Sleep is controlled by two processes, a homeostatic process and a circadian pacemaker. Entrainment of the circadian pacemaker is responsible for the appropriate timing of sleep and wakefulness relative to the environment. The development of a normal sleep/wake cycle requires the development and entrainment of the circadian pacemaker. Previous work of this project has shown in hamsters that the pacemaker begins before birth and is entrained by rhythmicity of the mother. Similar timing in humans would mean that the fetal pacemaker is functioning and is influenced by maternal rhythms throughout most of gestation. The goal of the proposed project is to better understand the physiology of the fetal pacemaker and understand how it is influenced by maternal rhythms, including the long-term consequences of abnormal entrainment. By measuring recently discovered molecular components of the pacemaker, we will test hypotheses about the similarities and differences between the developing and mature pacemaker and about the regulation of these molecules during development. We will specifically examine the physiological significance of maternal melatonin and the long-term effects of maternal entrainment. The project will better our understanding of fetal pacemaker regulation and the importance of the environment under which it develops.